Digital multi-train control with bi-directional data transmission in model railways

ABSTRACT

A method and device which digitally controls moveable and/or stationary electrical consumers in a model railway. The power for the consumers is supplied over the track in the form of a square wave voltage signal which is frequency and/or pulse width modulated according to digital control information for the consumers generated by a central control unit of the model railway. A consumer, after having received a control information addressed to said consumer, applies a return signal to the track, which return signal has a higher frequency than the frequency of the modulated square wave voltage. This return signal is detected by synchronizing the detection to the square wave voltage such that the return signal is detected in periods of the square wave voltage signal which are free of signal edges.

CROSS REFERENCES TO RELATED APPLICATIONS

[0001] This application claims priority to German Patent Application 10011 978.6 filed on Mar. 11, 2000.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] Not Applicable

BACKGROUND OF THE INVENTION

[0003] In digital controls for model railways, digital information and,at the same time, the power supply voltage are transmitted via the sameconnection line, namely the track, from a central control unit tovarious individual electrical consumers. The control unit modulates thepower supply voltage with a control signal for a decoder in eachconsumer. Moveable electrical consumers in the form of locomotives thusreceive an address, a desired speed, actuating, switch and controlinformation, or the like, as digital information. The decoders in theconsumers which serve as receiving means for the digital informationdecode the control signals and control a motor or switching devices withthe energy which is also transmitted via the track.

[0004] In the case of a stationary decoder, the same principle applies.In this case, a fixed wiring is used which is connected to the track.Stationary consumers are, for example, turnouts which are supplied withpower, as well as, with control signals using the track voltage, andwhich are provided with an appropriate decoder for decoding the controlsignals.

[0005] This type of voltage transmission for the purpose of power supplyas well as control, has always been unidirectional from the control unitto the consumer. Contact via the track, as is known, is subject topossible bad track contacts, bogeys, wheels, bad contact at turnouts andthe like. The switching processes and transients in the decoders, aswell as the wave form of the combined control and track supply signalitself can cause great interference and distortions with correspondingharmonics. As a result of these circumstances, the decoder in alocomotive might not receive the control signal at all, and on the otherhand, a received control signal could be so distorted so that it can notbe decoded correctly.

SUMMARY OF THE INVENTION

[0006] An object of the invention is to provide a method and device forthe digital control of moveable and stationary electrical consumers of amodel railway, which provide a more reliable control with limitedtechnical effort while allowing for the relevant control norms andstandards.

[0007] This object is solved by the subject matter of the independentclaims. Further advantageous developments are defined in the subclaims.The invention as claimed provides a digital multi-train control withbi-directional data transmission between the consumers and the modelrailway's central control unit. The bi-directional data transmissionenables information to be sent from the consumer which information inthe simplest case, represents an acknowledgement or receipt of thetransmission of control information.

[0008] According to the main object of the invention there is provided amethod for digital control of electrical consumers in a model railwaywherein power for the consumers is supplied over the track in form of asquare wave voltage signal which is frequency and/or pulse widthmodulated according to digital control information for the consumersgenerated by a central control unit of the model railway, and wherein aconsumer, after having received a control information specificallyaddressed to said consumer, applies a return signal to the track, whichreturn signal has a higher frequency than the frequency of the modulatedsquare wave voltage, and wherein this return signal is detected bysynchronising the detection to the square wave voltage such that thereturn signal is detected in periods of the square wave voltage signalwhich are free of signal edges. The consumers can be moveable and/orstationary electrical consumers.

[0009] A fundamental problem is solved in the invention. It is, inprinciple, very difficult to return or feed back a data signal from thedecoder of a consumer to a control unit via the same transmission pathas the track power supply. This is due to the above mentioned signaldistortion within this transmission path and the resulting stronginterference effects and distortions in the signal to be returned or fedback to the control unit. It is likewise very difficult to successfullydecode the returned data, for example, in the form of an acknowledgementor receipt of a control signal. On the one hand, the control signal fromthe control unit, which is superimposed on the power supply voltage asfrequency modulation or pulse width modulation in a predefined manner,is always transmitted and present, and must not by affected by thereturn signal. On the other hand, the strong control signal modulationin the track signal presents a problem for decoding the signal to bereturned. Moreover, this is made even more difficult by the fact thatparticularly the decoder of the moveable consumer must be small sizeddue to its predefined constructional design in the consumer. Therefore,providing any substantial additional signal generating and transmittingequipment is ruled out.

[0010] The inventional solution succeeds in superimposing a returnsignal to be sent or retransmitted to the control unit on the tracksignal by means of little additional technical features within a decoderwhich have to be provided to implement this superimposing. Furthermore,the generated return signal can be produced reliably and with littletechnical effort. A decisive feature here is that the signal isgenerated and detected in synchronized manner to the modulated tracksignal such that the return signal can only be detected in signalperiods of the track signal which do not comprise signal edges, and, inother words, in signal periods or signal intervals between alternatingpolarities.

[0011] Preferably, the time sections of the modulated track signal beingused for superimposing the return signal are time sections in which thevoltage level of the digital track signal does not change. Preferably,these sections correspond with the second signal half of a zeroinformation in the digital track signal, as shown below. These periodsare detected by the decoder's evaluator means when detecting the digitaltrack signal anyway, so that a corresponding control or trigger signalcan be derived from the evaluator unit for generating the return signalwithout extra effort.

[0012] The return or feedback signal itself is a high frequency signalwhose frequency is considerably higher than the modulation frequency ofthe track signal. Such a high frequency signal can be detected reliablyin the above mentioned signal edge free periods between alternatingpolarities of the track signal. The criteria for this are explainedbelow referring to the disclosed examples. The signal form of the returnsignal to be superimposed on the track signal is not restricted tospecific wave forms. For example, the digital track signal can besuperimposed with a 1 MHz oscillation generated by an oscillator.Preferably, a cost-effective and space-saving current modulation is usedrather than a voltage coupling by means of an oscillating circuit orcapacitors.

[0013] In principle, the high frequency return signal can also becoupled into signal sections of the track signal which are not free ofsignal edges by the consumer, since, as recited in claim 1, upon receiptof the return signal, the signal periods which comprise signal edges arecut off. In this way, the oscillating circuits or the active filters ofhigh quality in the detection means for the return signal, which aretuned to the return signal's frequency, remain unaffected by the controlsignal edges of the square wave track signal. However, it isadvantageous when the return signal is exclusively generated in thepredefined edge free periods of the track signal. Thereby, the lostpower is kept to a minimum.

[0014] An addressed consumer, to which control information is sent ortransmitted in a track voltage data packet cannot only acknowledge thereceipt of the control information by generating the return signalintermittently or continuously and preferably in the next data packet.The consumer can even send more information in several of the periodsbetween signal edged or alternating polarities available in the nextdata packet, as explained in detail below.

[0015] The next data packet is preferably used for transmitting thereturn signal because this guarantees that the return signal is clearlyallocated to the returning consumer which was addressed in the previouspacket so that a separate address in the return signal is not necessaryto identify the returning consumer which generated the return signal.

[0016] As a result of the receipt message provided by the return signal,the control through the central control unit becomes more secure againstthe above mentioned influence by signal interference and distortion.Multiple transmissions of the same control information for one consumercan be avoided. Hence, lots of control information for a number ofconsumers can be managed, thereby increasing the transmission bandwidthof the control unit. As a result of the bi-directional communicationaccording to the invention, it is also possible to transmit consumerdata to the central control unit via the track, alongside thetransmission of supply energy and control information, at the same timeas transmitting control information to the consumers.

[0017] In addition, the invention offers a simple way to localizemoveable consumers on the model railway. For this purpose, the track issubdivided into several sections, with an evaluation unit allocated toeach section.

[0018] The invention has been implemented for data transmission in theNMRA DCC Electrical Standard and NMRA DCC Communication Standard,however, it can also be used for other forms of digital transmission ofinformation from a control unit to a consumer in a digital model railwayif energy is simultaneously supplied via the same wiring or transmissionmeans as the control information. For example, this is the case forstandards with pulse width or pulse length modulation instead of thefrequency modulation used in the preferred embodiment. Typically,regardless of the standard, an information packet sent to a consumercontains its address so that the data's addressee is clearly defined.The invention, however, could also be used in principle with a controlsystem where a fixed number of possible consumers receive information ina prescribed addressing cycle.

[0019] An evaluation means for the return signal from the consumer can,for example, be integrated into a power amplifier or into the controlunit on the railway, or can be provided as an independent additionaldevice. The evaluation means synchronizes the data from the returnsignal which the consumer sends by detecting and evaluating the returnsignal together with the track signal which the control unit transmits.As a result of this, the synchronisation of the consumer's return signalis achieved. Synchronisation can also be achieved by sending a specificsynchronisation signal from the control unit directly to the evaluationmeans. In this way, the answer from a specific consumer can betriggered.

[0020] Furthermore, in principle, it is also possible to implement theinvention by generating a constant additional high frequency signal inthe track signal corresponding to the frequency of the above returnsignal and, instead of generating the return signal, a “returning”consumer would temporarily damp or suppress this continuous highfrequency signal. For detecting such a signal suppression, theevaluation means can also comprise a sender or transmitter whichconstantly modulates a sender frequency, e.g. 1 MHz, on the trackvoltage and which monitors the amplitude of the modulated voltage.Synchronisation of the return signal can be realized as described above.A consumer which transmits a return signal to the evaluation unit loadsthe track voltage during the predefined transmitting or sending periodsby lowering its impedance at 1 MHz. The evaluation unit detects theresulting amplitude decrease and recognizes a return signal. Thereby, abinary transmission of information from the consumer to the control unitis also possible by means of repeated load and non-load actions effectedin the preferred predefined time periods.

[0021] These and still other objects and advantages of the presentinvention will be apparent from the description which follows. In thedetailed description below, preferred embodiments of the invention willbe described in reference to the accompanying drawings. Theseembodiments do not represent the full scope of the invention. Rather theinvention may be employed in other embodiments. Reference shouldtherefore be made to the claims herein for interpreting the breadth ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 shows the coding of bits with a track voltage formataccording to the NMRA standard, with possible time periods for a returnsignal according to an embodiment of the inventional method;

[0023]FIG. 2 shows a data packet with a track voltage format accordingto the NMRA standard;

[0024]FIG. 3 shows a schematic diagram to explain the principle of theinvention.

[0025]FIG. 4 shows a block diagram of a consumer adapted to perform theinventional method;

[0026]FIG. 5 is a block diagram showing an evaluation means according toan embodiment of the invention;

[0027]FIG. 6 shows diagrams of signals occurring at several points inthe block diagram of FIG. 5;

[0028]FIG. 7 shows an example of a detection circuit to be used in theembodiment of FIG. 5; and

[0029]FIG. 8 shows a block diagram for another example of an evaluationmeans according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0030] When transmitting digital information according to the NMRAstandard from a control unit 10 to a decoder or consumer 20 (locomotivedecoder or stationary decoder according to FIG. 3), the schemata in FIG.1 is used to code the bit values 0 and 1 in which possible time pointst[send] for return signals according to the invention are indicated. Adata packet transmitted in that manner is shown in FIG. 2. The preambleis a header for a data packet and consists of a sequence of at least ten“1” bits. The packet start bit is the first “0” bit which follows thepreamble. It concludes the preamble and signals that the next bitsrepresent an address byte. After transmission of the address byte, thereis another “0” bit as indication for a following data byte in the formof a data byte start bit. The error detection byte serves to recognizetransmission errors. The packet end bit at the end of a data bytedenotes the end of the data packet and generally belongs to the preambleof the following packet.

[0031] In the example, the evaluation unit 30 receives the track signalshown in FIG. 1 and 2 from the control unit 10. The consumer 20constantly detects and evaluates the track signal in a principally knownmanner and evaluates and carries out the control information containedin the data packets addressed to it. In this way, both the evaluationmeans 30 and the consumer 20 can use the square wave in the track totrigger and time the generation and detection of the return signal. Theevaluation unit 30 supplies the return of feed-back information in thetrack signal detected by it to the central control unit 10 for furtherprocessing.

[0032]FIG. 2 shows a possible return or feed-back transmission of a byteaccording to the track format in FIG. 1. If a consumer 20 has fullyreceived a data packet addressed to it, this consumer can feed backinformation via the evaluation unit 30 to the control unit 10 in thefollowing data packet. For this purpose, the consumer 20 modulates theabove mentioned higher frequency on the data packet, which theevaluation means 30 then demodulates again and in thereby detects a bitinformation of the return or feed-back signal.

[0033] In the present example, a frequency of 1 MHz is used for thereturn signal which is far higher than the frequency of the track signalof 5 to 10 kHz. Moreover, the return signal according to FIG. 1 is sentduring the second signal half of a zero information (“0” bit), sinceduring this period, the digital track signal modulated by the controlunit for a longer period of time does not exhibit a change in signallevel, whose signal edges could lead to incorrect evaluation. By meansof this triggering when producing the return signal and particularlywhen detecting the return signal, the signal distortions andinterference present in the track signal itself are eliminated andinhibited from reaching the detection oscillating circuits, detectionfilters and detection counters in the evaluation means, which aresensitively tuned to the 1 MHz return signal.

[0034] The available signal edge free periods between alternatingpolarities in the form of the second half of the zero information islong enough, compared to the short periods of the return signal, so thatthe return of feedback signal can reliably be detected in oscillatingcircuits used in the evaluation means 30. The oscillating circuits haveenough time to oscillate to the main frequency and to detect the bitvalue 1 which represents a return signal according to the presentembodiment. The bit value 0 represents that the transmission frequencyof the sender frequency in the consumer's return signal is not present.Besides, another allocation of the detection and non-detection of thereturn signal to the bit values 0 or 1 can be freely set. In order toachieve the highest quality, the NMRA track format has the possibilityto introduce stretched “0” bits as indicated in FIG. 1. Thereby, theperiod of the second zero bit half can even be lengthened.

[0035] In order to implement the described method, it is necessary thatall consumers which momentarily do not send a return signal have a highimpedance for the selected transmission frequency (here, for 1 MHz).Depending upon the detection means in the evaluation means, it is alsopossible to select considerably lower frequencies, for example, down to300 kHz or even lower, for the return signal. In this case hardwareexpenditure may be higher and it might be necessary to lengthen thesignal edge free periods between alternating polarities being used fortransmission and detection of the return signal. Alternatively,frequencies higher than 1 MHz are also possible for the return signal.

[0036] The track signal format in FIG. 1 and 2 shows at least elevenzero bits due to the use of the error correction byte in a valid datapacket. Thus it is possible to transmit from the consumer more than only1-bit information as a return signal which, in the simplest case,represents confirmation of receipt of the control signal. Allowing forthe synchronisation bit, at least ten data bits can be transmitted inthe return signal to the control unit. Of these, only eight bitscorresponding to one byte are suitably used. Therefore, it is possible,provided corresponding sensors are installed in the locomotives andother consumers, to transmit information about the current speed,acceleration, temperature and energy consumption of the driving motor orthe energy consumption of stationary consumers and the like to thecontrol unit.

[0037] According to FIG. 4, a 1 MHz oscillator 40 is provided inconsumer 20. The oscillator receives an oscillation enable signal from ascanning device 50 which scans the track signal and produces asynchronising signal to the predefined track signal period used. In thisexample, this period is the second half of the zero bits in the datapacket following the data packet addressed to the consumer 20. Uponreceipt of the oscillator enable signal, the oscillator 40 drives anotherwise open transistor switch 60 with 1 MHz.

[0038] The switch 60 is connected to the track in series via a workingimpedance Z. In the diagram, the impedance is provided behind arectifier 70 which serves to supply energy to the consumer 20 as inknown in the art. The series circuit of impedance Z and switch 60 canalso be directly connected to the track. In the example shown in FIG. 4,the track voltage is superimposed by means of a current modulation withthe return or feedback signal. This solution is technically simple andspace-saving. The aforementioned necessary high impedance of anon-sending consumer for the return signal frequency is guaranteed bythe inherent hardware of the consumer which is realized when switch 60is open, i.e. disabled.

[0039] According to FIG. 5, the evaluation means 30 includes a detector31 in the power circuit, which is supplied with the track signal. Thesquare wave signal according to FIG. 1 generated by the control unit isrepresented in FIG. 6a and indicated in FIG. 5. The track signalexhibits a number of signal distortions and interference as explainedabove, as well as a possibly existing return or feedback signal. In FIG.6a, the return signal is located in the signal edge free periods betweenalternating polarities marked R of the modulated control voltage fromthe control unit 10. The detector 31 obtains a detection signal from thetrack signal according to FIG. 6b. A subsequent signal limiting andpre-amplifying circuit 32 provides the normalized detection signalaccording to FIG. 6c, in which the return signal already occurs moreclearly.

[0040] A gate switch 34 connected to the signal limiting andpre-amplifying circuit 32 is provided in the form of an analogue switch,and filters out the time periods R used for the return signal from thenormalized detection signal according to FIG. 6c. For this, the controlcontact of the gate switch 34 receives a synchronisation signal from asynchronisation device 33. The synchronisation device 33 has the sameprinciple construction as a sensor device 50 and receives the controlsignal sent to the track by the control unit 10 according to FIG. 1.Alternatively, the track signal according to FIG. 6a can also be sensedby the synchronisation device 33. As a result of this synchronisation,it is ensured that a filter amplifier 35, here in the form of a highquality active band pass, which is tuned to 1 MHz, receives the reducedsignal according to FIG. 6d. The output signal of the filter amplifier35 according to FIG. 6e is demodulated in a demodulator 36. Thedemodulated signal according to FIG. 6f is compared in a comparator 37with a threshold value and the output signal according to FIG. 6g issupplied to the control unit 10.

[0041]FIG. 7 shows a preferred embodiment for the detector 31, accordingto which a measuring resistance is provided in a connection line fromthe control unit 10 to the track. The measuring resistance converts theexisting track signal with or without superimposed return signal to aproportional voltage. The voltage measured over the measuring resistanceis pre-filtered in a band pass and supplied to the signal limiting andpre-amplifying circuit 32, which has been provided as a differentialamplifier. Otherwise, FIG. 7 corresponds to FIG. 5.

[0042]FIG. 8 shows an alternative in which a detector 31′ is a measuringsensor which, for example, contains a differentiator which converts thesquare wave return signal contained in the detected signal into a pulseseries. A counter 38 synchronized to the signal periods R by the switch34 counts the pulses in each time period R. Furthermore, the counter 38is controlled by the synchronisation device 33 such that it is set tozero outside the time periods R, and counts the pulses during the timeperiod R. For this purpose a gate switch is used. Apart from the pulseseries resulting from the return signal, the counted pulses can also bevarious interference pulses. As a consequence of the predefined highfrequency of the return signal's pulse series, these interferencepulses, however, can be neglected in case of a sufficiently high countvalue. In this way, if the counter has counted, for example, up to 64pulses, it can reliably be concluded that the counted pulses mainlyresult from the return signal and are not caused by interference andother sporadic signal distortions. Besides, considerably lowerfrequencies for the return signal are also sufficient to “lift” thecount value resulting from the return signal above contributions of theinterference signals in the overall count value.

[0043] A subsequent digital comparator 39 compares the count value ofdetector 30 with a set point value at the end of the time period R. Ifthe count value exceeds the set point value, the comparator 39 generatesa signal which represents a detected return signal during the timeperiod R. The comparison control in the example is performed such that apossible detected return signal is transmitted to the control unit aslong as the comparison control no longer transmits a release signal tothe comparator 39.

[0044] As another alternative, it is also conceivable not to use a highfrequency square wave modulation as return signal according to FIG. 4.Instead, a correspondingly high frequency pulse series generated by theconsumer as return or feed back signal can be directly coupled to thetrack and then detected using principle of FIG. 8.

[0045] In the implemented embodiments the following hardware componentsand parameters have been used:

[0046] Control unit 10: LZ100 with an amplifier LV101, both of LenzElektronik GmbH;

[0047] Decoder 20: LE103XF of Lenz Elektronik GmbH;

[0048] Transistor switch 60: PMBF170 of Philips;

[0049] Gate switch 34: CD4066;

[0050] Comparator 37: LM393;

[0051] Counter 38: 74HC393;

[0052] Value of impedance Z 330 Ohm; and

[0053] Value of measuring resistance of detector 31=0,15 Ohm.

[0054] While there has been shown and described what are at presentconsidered the preferred embodiment of the invention, it will be obviousto those skilled in the art that various changes and modifications canbe made therein without departing from the scope of the inventiondefined by the appended claims.

I claim:
 1. A method for digital control of electrical consumers in amodel railway, wherein the power for the consumers is supplied over thetrack in the form of a square wave voltage signal which is frequencyand/or pulse width modulated according to digital control informationfor the consumers generated by a central control unit of the modelrailway, wherein a consumer, after having received a control informationaddressed to said consumer, applies a return signal to the track, whichreturn signal has a higher frequency than the frequency of the modulatedsquare wave voltage, and wherein this return signal is detected bysynchronising the detection to the square wave voltage such that thereturn signal is detected in periods of the square wave voltage signalwhich are free of signal edges.
 2. The method according to claim 1 ,wherein the return signal is detected in signal edge free periods havingone and the same digital level.
 3. The method according to claim 1 ,wherein the return signal is detected in signal edge free periods which,due to the modulation, are relatively long periods, such as the secondsignal half of a zero information when using NMRA DCC electricalstandard and the NMRA DCC communications standard.
 4. The methodaccording to claim 1 , wherein the higher frequency return signal isapplied to the track and synchronized with the square wave voltage, andis in said signal edge free periods of the square wave voltage signal.5. The method according to claim 4 , wherein the higher frequency returnsignal is applied to the track in a data packet which follows the datapacket of the received control information.
 6. The method according toclaim 1 , wherein the return signal is superimposed to the track signalby means of a current modulation.
 7. The method according to claim 1 ,wherein the return signal is applied in the form of an oscillation andwherein the return signal is detected by detecting its frequency.
 8. Themethod according to claim 1 , wherein the return signal is applied inthe form of a series of pulses and wherein the return signal is detectedby counting a prescribed number of pulses.
 9. A device for digitalcontrol of electrical consumers in a model railway, wherein the powerfor the consumers is supplied over the track in the form of a squarewave voltage signal which is frequency and/or pulse width modulatedaccording to digital control information for the consumers generated bya central control unit of the model railway, comprising: means within aconsumer for applying, after having received a control informationaddressed to said consumer, a return signal to the track, which returnsignal has a higher frequency than the frequency of the modulated squarewave voltage; and means for detecting this return signal bysynchronising the detection to the square wave voltage such that thereturn signal is detected in periods of the square wave voltage signalwhich are free of signal edges.
 11. The device according to claim 10 ,wherein said means for applying said return signal comprise detectingmeans for detecting the square wave voltage signal and generating meansfor generating said return signal, said generating means being activatedby a synchronisation signal derived from the detector signal provided bythe detecting means for the square wave voltage, and wherein said meansfor detecting said return signal comprise an evaluation means connectedto the track and to the central control unit of the model railway. 12.The device according to claim 11 , wherein said evaluation means iscontrolled by a detection means which detects the modulated square wavesignal on the track.
 13. The device according to claim 10 , wherein saidmeans for detecting said return signal is controlled by means of asynchronisation signal from the central control unit, whichsynchronisation signal is synchronized with the modulated square wavesignal.
 14. The device according to claim 10 , wherein said means forapplying said return signal has an oscillator set to the frequency ofthe high frequency return signal which superimposes the return signal tothe track only in the signal edge free periods of the square wavesignal.
 15. The device according to claim 10 , wherein said means forapplying said return signal within a consumer has a series connection ofa working impedance and a switch means which is activated by anoscillator and is connected to the track.
 16. The device according toclaim 10 , wherein said means for detecting the return signal has afilter amplifier tuned to the frequency of the return signal, saidfilter amplifier being connected to the track via a detector for thesquare wave signal.
 17. The device according to claim 10 , wherein saidmeans for detecting the return signal has a resettable counter which isconnected to the track via a detector for the square wave signal. 18.The device according to claim 10 , wherein said means for detecting thereturn signal comprise a detector for the square wave signal which has ameasuring resistance or oscillating circuit.
 19. The device according toclaim 10 , wherein said means for detecting the return signal comprise ameasuring sensor for the square wave signal which has a differentiator.20. The device according to claim 18 , wherein a signal limiting andpre-amplifying circuit is connected to the measuring resistance oroscillating circuit.
 21. The device according to claim 19 , wherein asignal limiting and pre-amplifying circuit is connected to thedifferentiator.